There are many medical procedures in which tissue is treated or removed. For example, thermal therapy involving application of light or heat can be used for ablating or resecting tissue. Current thermal therapy procedures include microwave therapy, radio-frequency (RF) ablation, resection, and induction heating.
Microwave therapy involves the application of energy in the microwave frequency region to tissue to ablate the tissue. Devices for performing microwave therapy typically include a probe having a microwave antenna and a coaxial transmission line. Microwave therapy usually is performed as an outpatient procedure in a physician's office. One constraint of microwave therapy, however, is its poor ability to control the shape of the treated region by the physician. For example, when treating the prostate, the probe is positioned inside the urethra and the heat generated by the microwave energy pushes through the prostate while the urethra is being cooled. The amount of heat applied to the tissue, however, depends on the vascularity and density of the prostate tissue, thus making it difficult to control the size and shape of the treatment site.
RF ablation entails an electrode, connected to a power source, supplying radio frequency energy to tissue to ablate the tissue. RF ablation has been used conventionally for treating benign prostate hyperplasia (BPH), as well as for removing tumors. Typically, RF ablation requires surgical intervention and a multi-day hospital stay for the patient due to post-operative bleeding or retention.
Tissue resection also requires an electrode connected to a power source. The power source supplies alternating current to the electrode. The geometry of the electrode, (e.g., loop or wedge) allows a tissue chip to be carved as the electrode moves across a surface of the tissue. Tissue resection has been used conventionally in performing transurethral resection of the prostate.
Laser ablation involves application of a laser beam to vaporize tissue. This procedure can be very painful post-operatively as the procedure can sear nerve endings and cause charring of the tissue surface. When the tissue surface is charred, a greater amount of laser energy is necessary for deeper penetration into the tissue. Laser ablation thus has fallen out of favor with most physicians.
Induction heating typically involves implanting seeds inside a patient and exposing the patient to an oscillating magnetic field to cause the seeds to generate heat. The seeds are implanted inside a patient through surgery in advance. Treatment is subsequently performed in a physician's office by externally activating the seeds as the patient sits in an inductor chair that raises the temperature of the seeds through electromagnetic induction.
Conventionally, to implant the seeds, a medical operator places multiple seeds into a three-dimensional array with a needle using a two-dimensional grid pattern, and longitudinal spacing. A needle guide, called a template, typically defines the two-dimensional grid. The template includes a matrix of holes, which guide the longitudinal advancement of the needles to insure their proper two-dimensional positioning in the tissue. Subsequent to establishing the two-dimensional array of needles in the tissue, the medical operator deposits the seeds along the longitudinal axis of each needle. Biocompatible spacers typically space the seeds along the longitudinal axis of the needle. The medical operator alternately inserts spacers and seeds into the needle prior to placing the needle into the tissue. To maintain the position of the line of seeds and spacers as the needle is withdrawn, the medical operator typically employs a mandrel. This leaves a line of seeds in their proper longitudinal position. The medical operator then repeats this process at the other two-dimensional grid coordinates forming the desired three-dimensional array of seeds.
To provide effective heating over an elongated or wide target area, the seeds are typically uniformly and relatively closely spaced. The need to ensure accurate and precise implantation of numerous individual heating sources undesirably prolongs the procedure. Moreover, the use of discrete seeds requires an elaborate grid matrix for their proper implantation. This requirement is labor-intensive and costly. In addition, the discrete nature of the seeds renders them more susceptible to migration from their intended locations, thereby potentially subjecting the treatment site, and surrounding healthy tissue to over- or under-heating, reducing the effectiveness and reliability of the therapy.
In an attempt to accomplish a more even distribution of seeds in a longitudinal direction, the so-called “rapid strand” approach provides a bioabsorbable strand or suture onto which several seeds have been pre-assembled in a uniform spacing approximately 10 mm apart. Unfortunately, although spacing the seeds along the strand can generally provide a somewhat more uniform longitudinal dosage to the patient, the strand itself may not be sufficiently rigid to allow for it to be properly and reliably installed at the treatment site without becoming jammed in the delivery needles. Further, medical operators typically use 18-gauge bevel-tip needles to place seeds. Due to the bevel tip and flexibility of the hypodermic tubing of the 18-gauge needle, such needles tend to splay making it necessary for the medical operator to make multiple sticks to place the needle in the desired location.